Kibler Bertrand, Béjot Pierre
Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR6303 CNRS-UBFC, 21000 Dijon, France.
Phys Rev Lett. 2021 Jan 15;126(2):023902. doi: 10.1103/PhysRevLett.126.023902.
Multimode optical fibers are essential in bridging the gap between nonlinear optics in bulk media and single-mode fibers. The understanding of the transition between the two fields remains complex due to intermodal nonlinear processes and spatiotemporal couplings, e.g., some striking phenomena observed in bulk media with ultrashort pulses have not yet been unveiled in such waveguides. Here we generalize the concept of conical waves described in bulk media towards structured media, such as multimode optical fibers, in which only a discrete and finite number of modes can propagate. Such propagation-invariant optical wave packets can be linearly generated, in the limit of superposed monochromatic fields, by shaping their spatiotemporal spectrum, whatever the dispersion regime and waveguide geometry. Moreover, they can also spontaneously emerge when a rather intense short pulse propagates nonlinearly in a multimode waveguide, their finite energy is also associated with temporal dispersion. The modal distribution of optical fibers then provides a discretization of conical emission (e.g., discretized X waves). Future experiments in multimode fibers could reveal different forms of dispersion-engineered conical emission and supercontinuum light bullets.
多模光纤对于弥合块状介质中的非线性光学与单模光纤之间的差距至关重要。由于模式间非线性过程和时空耦合，对这两个领域之间过渡的理解仍然很复杂，例如，在块状介质中用超短脉冲观察到的一些显著现象在这种波导中尚未被揭示。在这里，我们将块状介质中描述的锥形波概念推广到结构化介质，如多模光纤，其中只有离散且有限数量的模式能够传播。这种传播不变的光学波包可以在叠加单色场的极限情况下，通过塑造其时空频谱线性生成，无论色散状态和波导几何形状如何。此外，当一个相当强的短脉冲在多模波导中非线性传播时，它们也会自发出现，其有限能量也与时间色散有关。光纤的模式分布随后提供了锥形发射的离散化（例如，离散化的X波）。未来在多模光纤中的实验可能会揭示不同形式的色散工程锥形发射和超连续光子弹。
